see sb.doing sth.变成被动语态怎么变呢?

see sb.doing sth.变成被动语态怎么变呢?

上面的那个人回答是不准确的,应该是sb.be seen to do sth.,要恢复不定式.我们的练习册上是这么说的.

sb. be seen doing
例如 they were seen playing footbal in the park.